1. Field of the Invention
The present invention is generally in the field of semiconductors. More specifically, the invention is in the field of fabrication of multilayer semiconductor structures with patterned and unpatterned layers.
2. Background Art
Bulk acoustic wave technology is rapidly emerging as a desirable technology for the fabrication of radio frequency filters used in today's radio frequency modules. Radio frequency filters based on bulk acoustic wave technology, as well as other semiconductor devices, typically include semiconductor structures having multiple, sequentially deposited layers of different materials. Some of these layers may be patterned using photolithographic and etching processes that are know in the art, while other layers in the structure, such as conformal over-coating layers, are unpatterned.
Depending on materials and patterning processes used, abrupt vertical steps can form in the regions of the semiconductor structure at the edges of the patterned layers. Such abrupt vertical steps can introduce undesirable effects in the semiconductor structures, such as high stress points, which are prone to cracking or delamination, voids in subsequent layers, mechanical discontinuities, which can cause undesirable oscillations in the structure, or pinch points in metal interconnect layers formed over the vertical steps. The vertical steps can be reduced by using complicated processes that involve backfilling of the voids left by the patterning process and/or using overcoating and polishing processes to eliminate the steps. However, such complex processes undesirably increase manufacturing cost.
Thus, there is a need in the art for a cost-effective method of reducing the effect of abrupt vertical steps in multi-layered stacks of patterned and unpatterned layers in semiconductor structures.